The present invention relates to methods and apparatus for performing medical procedures in the thorax of a medical or veterinary patient.
Some common medical procedures require the ability to operate on a specific location in the thorax, including locations in the respiratory system, such as the lungs, bronchi and immediately surrounding tissues. For example, needle aspiration biopsies have been performed heretofore using an endoscope inserted through the trachea into a bronchus. The needle is advanced through the endoscope through the bronchial wall to sample tissue in a lymph node within the lung parenchyma near the exterior surface of the bronchus. The physician can monitor placement of the endoscope and the biopsy needle using the optical system of the endoscope. As the endoscope is advanced toward the area to be sampled, the physician can determine where the tip of the endoscope lies by observing features of the airway itself. However, it is difficult to place a biopsy needle within a particular lymph node using this approach. The physician cannot see the lymph nodes, which lie outside of the airway. Therefore, the physician can only position the endoscope tip and the biopsy needle at an approximate position, near the location of the lymph node to be biopsied. For this reason, there has been a significant need for improvement in the reliability of needle aspiration biopsies of the lymph nodes surrounding the respiratory tract. There have been similar needs for improvement in other biopsies procedures using a probe advanced into the body, such as a biopsy needle or biopsy forceps to sample tissues in the vicinity of the respiratory tract. There have been similar needs for improvement in other procedures where a probe is advanced into the tissues of the thorax for other purposes as, for example, to perform surgical procedures on these tissues or to administer drugs within these tissues.
Some procedures heretofore have used imaging during advancement of the probe to provide guidance. Thus, as the probe is advanced, the probe and the body are imaged using conventional imaging techniques such as fluoroscopy or magnetic resonance imaging. This allows the physician to observe the relationship between the position of the probe and the surrounding tissues. These procedures have the disadvantage that the imaging apparatus is occupied for the entire time required to perform the procedure. Moreover, the use of fluoroscopic or other x-ray based imaging modalities during the procedure exposes the physician and the patient to radiation.
As described, for example, in U.S. Pat. Nos. 5,558,091, 5,391,199; 5,443,489; and in PCT International Publication WO 96/05768, the disclosures of which are hereby incorporated by reference herein, the position, orientation or both of the distal end of a probe can be determined by using one or more field transducers such as a Hall effect or magnetoresistive device, coil or other antenna carried on the probe, typically at or adjacent the distal end of the probe. One or more additional field transducers are disposed outside the body in an external frame of reference. The field transducers preferably are arranged to detect or transmit non-ionizing fields or field components such as a magnetic field, electromagnetic radiation or acoustical energy such as ultrasonic vibration. By transmitting the field between the external field transducers and the field transducers on the probe, characteristics of field transmission between these devices can be determined. The position and/or orientation of the sensor in the external frame of reference can then be deduced from these transmission characteristics. Because the field transducer of the probe allows determination of the position of the probe, such transducer is also referred to as a xe2x80x9cposition sensorxe2x80x9d.
As described, for example, in the aforementioned U.S. Pat. No. 5,558,091, the frame of reference of the external field transducers can be registered with the frame of reference of imaging data such as magnetic resonance imaging data, computerized axial tomographic data, or conventional x-ray image data. The probe position and orientation data derived by field transmission can be displayed as a representation of the probe superimposed on an image of the patient""s body. The physician can use this information to guide the probe to the desired location within the patient""s body, and to monitor its orientation during treatment or measurement of the body structure. This arrangement greatly enhances the ability of the physician to navigate the distal end of the probe through bodily structures. Because it does not require acquisition of an optical image of the surrounding tissues for navigation purposes, it can be used with probes which are too small to accommodate optical elements, and can be used for navigation of the probe within solid or semisolid tissues. The transducer-based system also avoids the difficulties associated with navigation of a probe by continuous imaging of the probe and patient during the procedure. For example, it avoids exposure to ionizing radiation inherent in fluoroscopic systems.
Some additional problems are encountered in use of systems of this type for procedures in the thorax near the respiratory system. As the patient breathes, the positions, sizes and shapes of the thoracic organs change. Thus, if an image of the patient is acquired at one stage of the respiratory cycle, the image data does not accurately represent the patient during other stages. Therefore, if the position of the probe is detected while the patient is in one stage of the respiratory cycle, and this probe position data is combined with patient image data from another stage of the respiratory cycle to provide an image with a representation of the probe superposed thereon, the location of the probe relative to the surrounding organs will be depicted inaccurately.
As described in International Publication WO 97/29709, the disclosure of which is incorporated by reference herein, problems of this nature can be avoided by positioning a first probe, referred to as a xe2x80x9csite probexe2x80x9d within the body of the patient at a location to be treated, and providing a further probe, referred to as an xe2x80x9cinstrument probexe2x80x9d for performing the medical procedure. The site probe is positioned within the body at the location to be treated as, for example, at a location to be biopsied. Using a location system such as the magnetic location systems discussed in the aforementioned patents, the locations of both probes are monitored during the medical procedure. Therefore, the distance and direction from the instrument probe to the site probe are known during the medical procedure, despite any motion caused by the patient""s breathing. Using that directional and distance information, the physician can navigate the instrument probe to the site probe.
PCT Publication WO 97/29682 refers to systems for determining the xe2x80x9cphysiological motionxe2x80x9d such as breathing motion or cardiac motion of a portion of the body in which a probe is situated. Using a device such as a belly strap to sense breathing motion, the system selects a xe2x80x9ccorrectxe2x80x9d image from a set of previously obtained images at each instant during the procedure, or interpolates between images. Thus, the displayed image always reflects the actual size and shape of the organs at the instant in question. Accordingly, the representation of the probe can be accurately superposed on the display image.
U.S. Pat. No. 5,577,502 discloses a system in which the position of the subject""s chest is monitored by devices such as optical, ultrasound or mechanical tracking elements. Based on that positional tracking, the image used in a superposition system is distorted so as to provide a corrected image which changes as the subject breathes. The position of the probe can be superposed on the corrected image. Systems of this type require considerable computation to distort the reference image as the patient moves through various stages of the respiratory cycle. Moreover, additional equipment is required for tracking the position of the patient""s chest. In an alternative approach also discussed in the ""502 patent, a series of images is acquired at numerous stages of the respiratory cycle. As the patient moves through different stages of the respiratory cycle, different images are employed. This approach multiplies the task of acquiring and storing the image data. Moreover, this approach can only be used if a set of multiple images exists. For example, where the patient is subjected to a conventional diagnostic imaging procedure such as an MRI or CT imaging, a single set of image data representing the patient at only one stage of the respiratory cycle generally is acquired. The need for a biopsy or other procedure using a probe advanced into the patient may only be apparent after that image has been evaluated. To acquire a series of images, the patient must be subjected to further imaging procedures before the interventional procedure using the probe can begin.
Thus, despite these and other efforts in the art, further improvements in interventional procedures and apparatus for performing the same would be desirable.
One aspect of the present invention provides methods of performing medical procedures on thoracic tissues, and particularly on tissues of the respiratory system or tissues adjacent the respiratory system. A method according to this aspect of the present invention includes the steps of providing an image of the patient in an image frame of reference representing the patient at a selected respiratory state, such as in a selected stage of the normal respiratory cycle, and advancing a probe into the respiratory system of the patient by adjacent tissues. During the advancing step, the disposition of the probe is determined in a locating frame of reference when the patient is at the aforesaid selected respiratory state. The disposition of the probe desirably is detected by transmitting one or more non-ionizing fields to or from at least one probe field transducer on the probe and detecting one or more properties of the transmitted fields. The method further includes the step of transforming the image, the disposition of the probe in the locating frame of reference or both so as to place the image and the disposition of the probe into a common frame of reference. Typically, the transforming step is performed by transforming the disposition of the probe in the locating frame of reference into the image frame of reference. The method further includes the step of displaying the image of the patient with a representation of the probe superposed thereon, at a location corresponding to the disposition of the probe in the aforesaid common frame of reference.
Because the disposition of the probe used as the basis for the superposed representation is acquired at the same stage in the respiratory state as the image, the motion artifact or inaccuracy caused by motion due to the respiratory cycle is eliminated. Methods according to this aspect of the invention thus provide a solution to the motion artifact problem which does not require acquisition of multiple images for massive manipulation of the image data to distort an image. The system is compatible with standard images acquired for diagnostic purposes, which represent only one stage in the respiratory cycle.
The method preferably further includes the step of detecting when the patient is in the selected stage of the respiratory cycle by monitoring the position of a reference point on a patient which moves in respiration. Preferably, the system detects when the patient is in the selected respiratory state by determining whether the position of the reference point matches a selected position corresponding to the selected respiratory state within a preselected tolerance. For example, where the image was acquired at a particular stage of respiration, the system acquires the disposition of the probe during each breath, at the same stage of respiration.The method may further include the step of establishing a particular position of the reference point which corresponds to a selected stage of the respiratory cycle by monitoring the position of the reference point over a plurality of respiratory cycles and finding an extreme position of the reference point which recurs in each cycle using the data acquired by this monitoring procedure. For example, the selected stage of the respiratory cycle may be the minimum inspiration state, i.e., the state achieved at the end of exhalation during a normal breathing cycle. In this case, the system may select the position of the reference point at which the patient""s front chest wall is closest to the patient""s back. If the patient is lying in a supine position with his or her back on a table, the system may select the position where a reference point on the patient""s front chest wall is closest to the table.
The step of monitoring the position of the reference point desirably includes the step of transmitting one or more non-ionizing fields to or from at least one reference field transducer on the reference point. Thus, the position of the reference point can be monitored using much of the same equipment and techniques as are used for monitoring the position of the probe.
Desirably, the system displays a perspective image of the tissues surrounding the probe as, for example, a perspective image of an airway and surrounding tissues with the probe superposed thereon. The image is displayed so that the position of the probe and the trajectory for moving the probe to engage a target location such as a lymph node is readily visible by viewing the displayed image. Typically, the step of advancing the probe is performed by advancing the probe through an airway as, for example, by passing the probe through the wall of the airway to sample tissue at a target location such as the lymph nodes outside of the airway. The probe may include an endoscope and a needle. The step of advancing the probe may be performed by advancing the endoscope until the endoscope is positioned at the wall of the airway adjacent the target location, and then advancing the needle through the wall of the airway.
During some portions of the probe-advancing step, the patient may be instructed to hold his or her breath at the prescribed respiratory state. Thus, while the patient holds the prescribed point in the respiratory state, the system will continually acquire new positions of the probe and will continually update the superposed representation of the probe on the image. If the patient momentarily deviates from the prescribed stage of the respiratory cycle, the system will stop generating new superposed positions of the probe representation on the image and preferably will provide a warning to the physician.
Further aspects of the present invention provide apparatus for monitoring the respiratory cycle of a medical patient. Apparatus according to this aspect of the invention desirably includes means for monitoring the position of a reference point on a patient which moves in the respiratory cycle and means for finding an extreme position of a reference point which recurs in each cycle based on the data acquired in the monitoring operation. The apparatus desirably further includes means for determining whether the position of the reference point matches such extreme position to within, a preselected tolerance. Apparatus according to this aspect of the present invention can be used in the aforementioned methods. Desirably, the means for monitoring the position of a reference point includes a reference field transducer adapted for mounting on the exterior of a patient""s thorax at the reference point and one or more external field transducers defining a locating frame of reference. The apparatus desirably further includes sensing means for transmitting one or more non-ionizing fields between the external field transducers and the reference field transducer, detecting one or more properties of the transmitted fields and determining the position of the reference field transducer in the locating frame of reference from the so detected properties. The apparatus may further include a probe adapted for insertion into the respiratory system of a patient of the surrounding tissues, and at least one probe field transducer on the probe. The sensing means desirably is operative to transmit one or more non-ionizing field between the external field transducers and the probe field transducers, to detect one or more properties of these transmitted fields and to determine the position of the probe field transducer in the locating frame of reference from these properties. As discussed above in connection with the methods, apparatus in accordance with this aspect of the present invention can utilize the same position measuring devices as employed in determining the probe position to determine the respiratory cycle.